Process of silver extraction.



UNITED srATns FRANCIS J. HOBSON, OF GUANAJUATO, MEXICO.

PROCESS OF SILVER EXTRACTION.

Specification of Letters Patent.

Patented Aug. 7,1;906.

Original application filed July 18, 1905, Serial No.,270,300. Dividedand this application filed December 20, 1905. .Serial No. 292,554.

To a whom, it may concern:

Be it known that I, FRANCIS J. HoBsoN, a citizen of the United States,residing at Guanaj-uato, in the Republic of Mexico, have inventedcertain new and useful Improvements in Processes of Silver Extraction,of which the following is a specification.

My present invention -consists of an improved process for extractingsilver from its ores, and particularly from ores in which the silver ispresent in combination with sulfur, sulfur bemg present in almost allsilver ores. The improved-process is of very general application.

Briefly outlined the process consists of treating the ores after suchpreliminary sizing as may bev desired with a solution contaming amercurous potassic cyanid. This salt, the characteristics of which aredescribed in my previous application, Serial No. 270,300,.filed July 18,1905, of which the resent case is a division, has a selective affinityfor silver in combination with sulfur. This selective affinity I havedemonstrated experimentally a great many times. The formula of the saltis KHgCy It forms with silver when in combination with sulfur a doublesalt, the cyanid .of silver and potassium, which is freely soluble inwater, and also the sulfid of mercury, which is substantially insolublein water, and passes off with the tailings. The reaction to which I hererefer is expressed verbally as follows: silver sulfid mercurous potassiccyanid cyanid of silver and potassium sulfid of mercury, and in chemicalsymbols the reaction is expressed thus:

AgS KH o KA c HgS.

The solvent which I'employ in my improved process does not attack goldin any of the forms in which it appears to exist in ore, and although itforms the same salt of silver and potassium in solution as cyanid ofpotassium when the latter dissolves silver it does not do so in the sameway, since potassium cyanid dissolves silver by the wellknown Elsnersequation, stated verbally as follows: silver cyanid of potassium oxygenwater cyanid of potassium and silver potassium hydrate or causticpotash. This equation in chemical symbols is stated thus:

2Ag 4KCy-lo H20 KAgCy, axon.

The same equation applies to-the solution of gold, gold replacing silverin it.

Free oxygen in solutionis necessaryto dissolve silveror gold and formthe doublesalt of potassium and silver or gold'with cyanogen.

I may produce the mercurous vpotassic cyanid in any .desired way, sincethe particular method of its production does :not seem tov affect theresults. Imay, for exam-. ple, add mercurous chlorid (Hg,Cl to asolution of potassium cyanid, '(KCy) An other methodwhich I may useis toadd mercuric chlorid (corrosive sublimate, HgCl to the ordinary millcyanid solutions containingv ferrocyanid of potassium, in which case thereaction may be stated verbally thus: ferrocyanid of potassium mercuricchlorid ferrocyanid of mercury]' chlorid of otassium. This reaction maybe expresse in chemical symbols as follows:

KFeO zn ol, Hgmec 4KC1.

This is succeeded by the following reaction: Ferrocyanid of mercurycyanid of potas sium ferrocyanid of mercury and potassium mercurouspotassic cyanid. This reaction may be expressed in chemical symbols asfollows:

The most suitable strength of the solution is to some extent dependentupon the silverl content of the ore and the form in which the metal isresent. I have obtained good results with solutions varying from .05 vto.50 per cent. The metal may be separated from the solution in any of theapproved methods commonly employed in cyanid processes, such asprecipitation by zinc dust or shavings or electrolysis.

The solution should be kept alkaline, and this my be eflected by theaddition of any suitable alkali, such as caustic potash or soda,although in most cases lime will be found to be not only the cheapestbut the best alkali.

I do not in this case claim specifically the formation of the mercurouspotassic cyanid by the addition of mercuric chlorid in a solutioncontaining a ferrocyanid, since that is covered by my pendingapplication, Serial No. 292,555, filed December 20, 1905, a di- Havingthus described my invention, what I claim, and wish to protect byLetters Patent of the United States, is

1. The rocess of extractin silver from its ores, which consists in subjecting the ores to the dissolving action of a solution of a mercuroussalt of cyanogen and an alkaline metal.

2. The process of extracting silver from its ores, which consists insubjecting the ores to the dissolving action of an alkaline solution ofa mercurous salt of cyanogen and an alkaline metal.

3. The process of extracting silver from its ores, which consists ofsubjecting the ores to the dissolving action of a solution of potassiumcyanid to which has been added mercurous chlorid.

4. The process of extracting silver from ores in which it is present incombination with sulfur, which consists in treating the ores with asolution of a mercurous salt of cyanogen and an alkaline metal, therebyforming a solution of cyanids of silver and the alkaline metal andprecipitating the sulfid salt of mercury.

5. The process of extracting silver from ores in which it is present incombination with sulfur, which consists in treating the ores with analkaline solution of potassium cyanid and mercurous chlorid, therebyforming a solution of the double cyanid of silver and potassium andprecipitating the sulfid salt of mercury, and then separating the silverfrom the solution.

6. The process of extracting silver from ores in which it is present incombination with sulfur, which consists in treating the ores with analkaline solution of mercurous potassic cyanid, thereby forming insolution the double cyanid of silver and potassium and precipitating thesulfid salt of mercury, and then separating the silver from thesolution.

7. The ores in which it is present in combination with sulfur, whichconsists in treating the ores with an alkaline solution of mercurouspotassic cyanid of strength between .05 and .50 per centum, therebyforming in solution the double cyanid of silver and potassium andprecipitating the sulfid salt of mercury, and

then separating the silver from the solution.

FRANCIS J. HOBSON.

, Witnesses:

Tnos. '0. YOUNG, H. D. OLEEDE.

roeess of extracting silver from

